Java 1.7 Features

7/26/2019 Java 1.7 Features

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Java 7: The Top 8 Features September 2, 2011 VineetManohar

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Its been a while sine the last ma!or "a#a releaseand e$petations were nat%rall& hi'h (or the%pomin' release…)

It*s been a while sine the last ma!or "a#a release and e$petations were

nat%rall& hi'h (or the %pomin' release) +he "a#a release initiall& inl%ded

man& "S-s with e$itin' (eat%res, like s%pport (or los%res, whih were later

de(erred to "a#a 8 in order to release "S-s that are alread& done) +his

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e.eti#el& dil%ted what is now o.ered in "a#a and has le(t some

disappointed)

+he "a#a lan'%a'e has %nder'one ma!or han'es sine I started %sin' it in

1998) Most o( the han'es were dri#en b& the "a#a /omm%nit& roess "/

whih was established in 1998 as a (ormal and transparent proess to let

interested indi#id%als and entities partiipate and in%ene how the

lan'%a'e sho%ld e#ol#e) +his is done thro%'h the s%bmission o( a han'e

re%est, known as "a#a Speiation -e%est "S-, (ollowed b& a re#iew and

a #otin' proess) /han'es or enhanements made to the lan'%a'e an be

%s%all& traked bak to a "S- where the& were ori'inall& p%t (orward (or

re#iew) 6or e$ample, the addition o( 7eneris in "a#a 5 was done #ia "S- 14)

Java Releases

ere*s a %ik snapshot o( the past "a#a release dates table 1) +here are

se#eral small new (eat%res and enhanements in "a#a ) %t o( the 28

(eat%res that I looked at, here are the ones that I (o%nd %se(%l)

New features and enhancements

#1 Strings in switch

In pro'rammin', we o(ten eno%nter sit%ations where we need to do

di.erent thin's based on di.erent #al%es o( a #ariable) 6or :oolean

#ariables, an i(;then;else statement is the per(et wa& o( branhin' ode) 6or



primiti#e #ariable t&pes we %se the swith statement) owe#er, (or Strin'

#ariables, we tend to resort to %sin' m%ltiple i(;then;else branhes as (ollows)

Java 6 and Before

ne workaro%nd (or this is to on#ert the Strin' into an en%m and then

swith on the en%m)

Java 7

"a#a , howe#er, has added a lan'%a'e le#el s%pport (or Strin' in swith)

<ow &o% an rewrite the same ode more ele'antl&=



<ot onl& does this help %s write more readable ode, b%t it also helps the

ompiler 'enerate more e>ient b&te ode as ompared to the i(;then;else

b& at%all& swithin' on the hashode and then doin' an e%als

omparison) lease note that &o% will 'et a <%llointer?$eption i( the

#ariable lan'%a'e in the abo#e e$ample resol#es to n%ll) I like this (eat%re,

b%t %nlike some o( the other enhanements in the past like 7eneri in "a#a

5, I don*t antiipate %sin' this (eat%re a lot) ratiall&, I nd m&sel( %sin' i(;then;else (or one or two #al%es and resort to an ?n%m when the n%mber o(

#al%es are hi'her)

#2 try-with-resources statement

ne o( the most %se(%l additions in "a#a is the a%to losin' o( reso%res like

Inp%tStream whih helps %s red%e boiler plate ode (rom o%r pro'rams)

S%ppose we were writin' a pro'ram whih reads a le and loses the

6ileInp%tStream when it*s done, here is how &o% wo%ld write the pro'ram=

ith Java 6 and Before



I want to point o%t a o%ple o( thin's in this ode) 6irstl&, notie that we

delare the 6ileInp%tStream o%tside the tr& blok !%st so that it an be

aessed in the nall& blok) +he seond obser#ation is that we need to

initiali@e the Inp%tStream to n%ll, so that it is '%aranteed to be initiali@ed

when we aess it in the nall& blok) Last b%t not the least, the is)lose in

the nall& blok ma& throw an ?$eption as well, thereb& hidin' the ori'inal?$eption thrown in the tr& blok ?$eption (rom the aller) Ahat we

probabl& want is to handle the ?$eption thrown (rom is)lose and throw

the ori'inal I?$eption)



+he abo#e ode still has a shortomin' that the ?$eption thrown (rom nall&

is s%pressed and not aessible to the allin' ode) I*m not s%re how o(ten

we want to 'et both the ori'inal ?$eption and also the ?$eption thrown

(rom the nall& blok, b%t i( we did want it, we o%ld do alwa&s do somethin'

like this=



S%ppressed?$eption abo#e is a %ser written "a#a bean with a eld named

s%ppressed o( t&pe ?$eption) +he allin' ode an then all

S%pressed?$eption)'et+hreadLoal)'et?$eption to 'et the ?$eption

that was s%pressed in the nall& la%se) 7reat, we sol#ed all the problems

assoiated with the tr&;ath;nall&B <ow we m%st remember to repeat this

e$at se%ene with eah %se o( tr&;ath;nall& when handlin' les or other

reso%res whih need to be losed) ?nter "a#a , and we an do the abo#e

witho%t the boiler plate ode)

ith Java 7



tr& an now ha#e m%ltiple statements in the parenthesis and eah statement

sho%ld reate an ob!et whih implements the new !a#a)lan')C%to/losable

inter(ae) +he C%to/losable inter(ae onsists o( !%st one method)

?ah C%to/losable reso%re reated in the tr& statement will be

a%tomatiall& losedB I( an e$eption is thrown in the tr& blok and another

?$eption is thrown while losin' the reso%re, the rst ?$eption is the one

e#ent%all& thrown to the aller) +he seond ?$eption is a#ailable to the

aller #ia the e$)'etS%pressed method) +hrowable)'etS%pressed is a new

method added on +hrowable in "a#a !%st (or this p%rpose)

!andatory catch "loc when using the try statement

<ote that i( &o% are reatin' C%to/losable reso%res in the tr& blok, &o% are

re%ired to delare a ath blok to ath the onrete e$eption thrown

(rom the at%al C%to/losable) lose method) Clternati#el& &o% need to

throw the ?$eption) +hink o( the lose method as impliitl& bein' alled as

the last line in the tr& blok) So, i( an appliation has its own C%to/losable

lass as (ollows=



+hen, the (ollowin' will a%se a ompile error=

+o $ the abo#e, &o% need to ath or throw the ?$eption (rom the allin'

method)



Synta$ for declaring multi%le resources

+he tr& statement an ontain m%ltiple statements separated b& semiolon)

?ah statement m%st res%lt in an C%to/losable ob!et)

It is ille'al to delare an& #ariable whih isn*t an C%to/losable)



&ut%ut

?---= tr&;with;reso%res not appliable to #ariable t&pe

re%ired= C%to/loseable

(o%nd= lon'

'uto(losa"le vs (losa"le

+he old /losable inter(ae introd%ed in "a#a 5, whih also has the same

method that now e$tends (rom C%to/losable, impl&in' that all /losable

lasses are a%tomatiall& C%to;/losable) +hose lasses a%tomatiall& beome

reso%res that an be reated in the tr& statement) +he sli'ht di.erene in

C%to/losable and /losable is that %nlike /losable)lose,

C%to/losable)lose is not s%pposed to be idempotent, whih means that

allin' it twie an ha#e side e.ets) +he seond di.erene is that sine

e$eptions thrown (rom C%to/losable) lose are s%ppressed,

C%to/losable)lose sho%ld not throw e$eptions whih an a%se problems

when s%ppressed, like the Interr%pted?$eption)

#) !ore %recise rethrow



+here are o(ten sit%ations when we want to ath m%ltiple e$eptions o(

di.erent t&pes, do Dsomethin'E with them, and rethrow them) Let %s

onsider this e$ample, where we ha#e some ode whih throws I?$eption

and SFL?$eption)

In the abo#e e$ample, we are lo''in' eah t&pe o( e$eption bein' thrown

b& the tr& blok be(ore rethrowin' them) +his res%lts in a d%pliation o( odein the ath bloks) :e(ore "a#a , to 'et aro%nd the ode d%pliation iss%e

we wo%ld ath the base e$eption as (ollows=

owe#er, this re%ires %s to rethrow the base ?$eption t&pe

!a#a)lan')?$eption (rom the allin' method)



p%bli stati #oid mainStrin'GH ar's throws ?$eption

ith Java 7

"a#a has added the Dpreise rethrowE (eat%re whih lets &o% ath and

throw the base e$eption while still throwin' the preise e$eption (rom the

allin' method)

<ote the ke&word nal in the abo#e ath la%se) Ahen a parameter is

delared nal, the ompiler statiall& knows to onl& throw those heked

e$eptions that were thrown b& the tr& blok and were not a%'ht in an&

preedin' ath bloks)

#* !ulti-catch

+here is no ele'ant wa& with "a#a J to ath m%ltiple e$eptions o( di.erent

t&pes and handle them in the same wa&)



Ko% an alwa&s ath the parent ?$eption in order to a#oid d%pliation o(

ode, b%t it is not alwa&s s%itable espeiall& i( the parent is

!a#a)lan')?$eption) "a#a lets &o% ath m%ltiple ?$eptions in a sin'le

ath blok b& denin' a D%nionE o( ?$eptions to be a%'ht in the ath

la%se)

<ote that the pipe * harater is %sed as the delimiter) +he #ariable e$* in

the abo#e e$ample is statiall& t&ped to the base lass o( ?$1 and ?$2, whih

is !a#a)lan')?$eption in this ase)

#+ Binary integral literals

Aith "a#a , &o% an now reate n%merial literals %sin' binar& notation

%sin' the pre$ D0bE



int n N 0b100000O

S&stem)o%t)printlnDn N E P nO

&ut%ut

n N 32

#6 ,nderscores in numeric literals

Aith "a#a , &o% an inl%de %ndersores in n%meri literals to make them

more readable) +he %ndersore is onl& present in the representation o( the

literal in "a#a ode, and will not show %p when &o% print the #al%e)

ithout underscore

int tenMillion N 10000000O

S&stem)o%t)printlnDCmo%nt is D P tenMillionO

&ut%ut

10000000

ith underscore

int tenMillion:%tMore-eadable N 10Q000Q000O

S&stem)o%t)printlnDCmo%nt is E P tenMillion:%tMore-eadableO

&ut%ut

10000000

!ore rules and e$am%les

1) /onse%ti#e %ndersores is le'al)

int n N 1000QQQQQQ000O



2) Rndersores an be inl%ded in other n%meri t&pes as well)

do%ble d N 1000Q000)0dO

lon' l N 1000Q000lO

int he$ N 0$deadQ0deO

int b&tes N 0$1000Q0000O

3) Rndersore an be inl%ded a(ter the deimal point)

do%ble e$ample8 N 1000Q000)000Q000dO

4) It is ille'al to start a literal with an %ndersore

5) It is ille'al to end a literal with an %ndersore)

J) It is also ille'al to ha#e %ndersore be !%st be(ore or a(ter a deimal point)



7 .m%roved ty%e inference for generic instance creation

"a#a 5 introd%ed 'eneris whih enabled de#elopers to write t&pe sa(e

olletions) owe#er, 'eneris an sometimes be too #erbose) /onsider the

(ollowin' e$ample where we are reatin' a Map o( List o( Strin')

ith Java + and 6

MapStrin', ListStrin'TT retVal N new ashMapStrin', ListStrin'TTO

<ote that the (%ll t&pe is speied twie and is there(ore red%ndant)

Rn(ort%natel&, this was a limitation o( "a#a 5 and J)

ith Java 7

"a#a tries to 'et rid o( this red%ndan& b& introd%in' a le(t to ri'ht t&pe

in(erene) Ko% an now rewrite the same statement b& %sin' the T

onstr%t)

MapStrin', ListStrin'TT retVal N new ashMapTO

+his does make the ode a little less #erbose) Ko% an also %se T onstr%t

when ret%rnin' a newl& reated ob!et)



+his, in m& opinion, 'oes onl& hal( wa&) +he (%ll sol%tion wo%ld ha#e been a

ri'ht to le(t (%ll t&pe in(erene)

Map map N new ashMapStrin', Strin'TO

+he abo#e wo%ld ha#e made the ode e#en less #erbose) +ho%'h this

enhanement an still be done in a later #ersion)

#/ !ore new .0& '.s for the Java %latform N.&23

C new set o( IU CIs and (eat%res were introd%ed in "a#a 1)4 %nder the

!a#a)nio paka'e) +his addition was alled the <ew IU CIs, also known as

<I) <amin' somethin' <ew is alwa&s short;si'hted bea%se it will notremain new (ore#er) Ahen the ne$t #ersion omes alon', what sho%ld the

new #ersion be alled, the <?A <?A IU "a#a 1) o.ers a rih set o( new

(eat%res and IU apabilities, alled <I)2 <ew IU #ersion 2) ere are the

ke& hi'hli'hts o( <I)2)

a3 acage

+he most important paka'e to look (or is !a#a)nio)le) +his paka'e ontains

man& pratial le %tilities, new le IU related lasses and inter(aes)

"3 4he 5avanioleath interface

ath is probabl& the new lass that de#elopers will %se most o(ten) +he le

re(erred b& the path does not need to e$ist) +he le re(erred to does not

need to e$ist) 6or all pratial p%rposes, &o% an think o( replain' !a#a)io)6ile

with !a#a) io)ath)

&ld ay

6ile le N new 6ileDhello)t$tEO

S&stem)o%t)printlnD6ile e$ists NN E P le)e$istsO

New ay



ath path N 6ileS&stems)'etWe(a%lt)'etathDhello)t$tEO

S&stem)o%t)printlnDath e$ists NN E P 6iles)e$istspathO

c3 4he 5avanioleiles class

+he 6iles lass o.ers o#er 50 %tilit& methods (or 6ile related operations whih

man& de#elopers wo%ld ha#e wanted to be a part o( earlier "a#a releases)

ere are some methods to 'i#e &o% a sense o( the ran'e o( methods o.ered)

X op& Y op& a le, with options like -?LC/?Q?ZIS+I<7, <6LLAQLI<[S

p%bli stati ath op&ath so%re, ath tar'et, /op&ption\ optionsO

X move3 Y mo#e or rename a le p%bli stati ath mo#eath so%re, athtar'et, /op&ption\ optionsO

X new.n%utStream3 Y reate inp%t stream p%bli stati Inp%tStream

newInp%tStreamath path, penption\ optionsO

X read'llBytes3 Y similar to the Cpahe IRtils)read6ile;+o:&teCrra& p%bli

stati b&teGH readCll:&tesath path throws I?$eptionO

X createSym"olic8in3 Y reates a s&mboli link, i( s%pported b& the le

s&stem p%bli stati ath reateS&mboliLinkath link, ath tar'et,

6ileCttrib%teT\ attrs throws I?$eption

d3 atchService '.

AathSer#ie CI is a new (eat%re introd%ed in "a#a 1)) It pro#ides an CI

that lets &o% DlistenE to a ertain t&pe o( le s&stem e#ents) Ko%r ode 'etsalled a%tomatiall& when those e#ents o%r) ?$amples o( e#ent t&pes are

apt%red b& StandardAath?#ent[inds lass)

X ?<+-KQ/-?C+?=an entr& is reated or renamed in the diretor&

X ?<+-KQW?L?+?=an entr& is reated or renamed o%t o( the diretor&

X ?<+-KQMWI6K=a diretor& entr& is modied



?$ample

ere*s a (%ll e$ample o( how to wath a diretor& and print an& newl&

reated les)

-%n the abo#e pro'ram) +hen reate a le new)t$t* in the diretor& lo's*)

+he pro'ram will print=



lo's= new le reated new)t$t

Note a"out atchService im%lementation

+he implementation will take ad#anta'e o( nati#e s%pport (or le han'e

notiation when s%pported b& the nati#e le s&stem, b%t will resort to

pollin' otherwise)

.9: Su%%ort

"a#a s%pport is now a#ailable in <et:eans and Intelli") ?lipse does not

s%pport "a#a &et) +he %pomin' release o( ?lipse 3) will not ha#e s%pport

(or "a#a either, b%t s%pport will be added in 3) S-1, e$peted September2011 table 2)

(onclusion

"a#a o.ers man& small lan'%a'e enhanements and (eat%res) owe#er, I

did not nd an& (eat%re as ompellin' as -e'e$ enhanement in "a#a 1)4 or

7eneris, C%to;bo$in' or ?n%m enhanement in "a#a 1)5) I nd the tr&;with;

reso%res enhanement parti%larl& %se(%l and am lookin' (orward to %sin'

it) I also look (orward to %sin' new (eat%res (rom the <I)2 librar&) #erall, I

am 'lad that somethin' was released this &ear as opposed to releasin' a

monolith o( han'es ne$t &ear)

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Java 1.7 Features